Switchable single-start or multi-start scroll pump
The present invention is a scroll pump comprising two intermeshing scrolls arranged so that on relative orbital movement of the scrolls gas is pumped from an inlet to an outlet. The scrolls have a plurality of successive scroll wraps I, II, II, IV, V, VI between the inlet and the outlet. There is a single-start condition in which fluid is pumped from the inlet to the outlet along a single flow path extending through each of the scroll wraps in succession and a multi-start condition in which fluid is pumped from the inlet along a plurality of flow paths which extend in parallel through radially adjacent scroll wraps and converge to a single flow path prior to the outlet. A valve arrangement is operable for switching the scroll pump between the single-start and the multi-start conditions.
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This application is a national stage entry under 35 U.S.C. §371 of International Application No. PCT/GB2013/051513, filed Jun. 10, 2013, which claims the benefit of G.B. Application 1211997.0, filed Jul. 5, 2012. The entire contents of International Application No. PCT/GB2013/051513 and G.B. Application 1211997.0 are incorporated herein by reference.
TECHNICAL FIELDThe present invention relates to a scroll pump comprising two intermeshing scrolls arranged so that on relative orbital movement of the scrolls gas is pumped from an inlet to an outlet.
BACKGROUNDA prior art scroll compressor, or pump, 100 is shown in
The fixed scroll 112 comprises a scroll wall 118 which extends perpendicularly to a generally circular base plate 120. The orbiting scroll 122 comprises a scroll wall 124 which extends perpendicularly to a generally circular base plate 126. The orbiting scroll wall 124 co-operates, or meshes, with the fixed scroll wall 118 during orbiting movement of the orbiting scroll. Relative orbital movement of the scrolls causes a volume of gas to be trapped between the scrolls and pumped from the inlet to the outlet.
A more detailed view of the scroll arrangement is shown in
Again, the scrolls have six successive scroll wraps I, II, III, IV, V, VI between the inlet 128 and the outlet 130. During relative orbiting motion of the scrolls, fluid conveyed through the inlet 128 is trapped initially in pockets formed in both the first wrap I and the second wrap II thereby forming two fluid flow paths starting at start points 132, 134. This fluid is forced along both flow paths and converges at convergence point 136 forming a single flow path from the convergence point to the outlet 130 through scroll wraps III, IV, V, VI. A multi-start arrangement is typically used when increased pumping capacity is required, that is when it is required that a greater volume of gas is pumped through the pump. Increased pumping capacity is achieved because fluid is pumped directly from the inlet 128 through two wraps I, II rather just a single wrap for a single-start arrangement. However, it will be appreciated that fewer wraps act as compression stages as compared to a single-start arrangement and therefore the ultimate pressure which can be achieved in a multi-start arrangement is less than with a single-start arrangement.
Looking first at the chamber pressure plots 140, 144 it will be seen as indicated above that after an initial pressure decrease to 100 mbar, which both single-start and two-start achieve at a similar rate, the two-start arrangement reduces pressure at a faster rate than the single-start arrangement. However, the single-start arrangement produces a lower ultimate pressure (0.005 mbar) than the ultimate pressure achieved by the two-start arrangement (0.01 mbar).
The power 142 consumed by the two-start arrangement is greater than that the power 138 consumed by the single-start arrangement over the initial period from 1000 mbar to 100 mbar, but subsequently the power consumed by the two-start arrangement is less than that consumed by the single-start arrangement.
Depending on the particular pressure regime required in a chamber evacuated by a vacuum pump, a pump with an appropriate configuration is selected. For example, if a low ultimate pressure is the most important characteristic, a single-start pump is used or if rate of pressure reduction is the most important characteristic a two-start pump is used.
Typically, the power consumption of a pump is reduced by limiting the inlet capacity or avoiding high compression ratios. A pressure relief valve is sometimes used in a two-start pump to reduce power consumption.
SUMMARYThe present invention provides a scroll pump comprising two intermeshing scrolls arranged so that on relative orbital movement of the scrolls gas is pumped from an inlet to an outlet, the scrolls having a plurality of successive scroll wraps between the inlet and the outlet, the scroll pump having a single-start condition in which fluid is pumped from the inlet to the outlet along a single flow path extending through each of the scroll wraps in succession and a multi-start condition in which fluid is pumped from the inlet along a plurality of flow paths which extend in parallel through radially adjacent scroll wraps and converge to a single flow path prior to the outlet, and a valve arrangement operable for switching the scroll pump between the single-start and the multi-start conditions.
The present invention also provides a scroll pump comprising two intermeshing scrolls arranged so that on relative orbital movement of the scrolls gas is pumped from an inlet to an outlet, the scrolls having a plurality of successive scroll wraps between the inlet and the outlet, the scroll pump having a first multi-start condition in which fluid is pumped from the inlet along a first plurality of flow paths which extend in parallel through radially adjacent scroll wraps and converge to a single flow path prior to the outlet and a second multi-start condition in which fluid is pumped from the inlet along a second plurality of flow paths which extend in parallel through radially adjacent scroll wraps and converge to a single flow path prior to the outlet, the number of starts in the first multi-start condition being different from the number of starts in the second multi-start condition, and a valve arrangement operable for switching the scroll pump between the first and the second multi-start conditions.
In order that the present invention may be well understood, some embodiments thereof, which are given by way of example only, will now be described with reference to the accompanying drawings, in which:
A scroll compressor, or pump, 10 is shown in
The fixed scroll 22 comprises a scroll wall 28 which extends perpendicularly to a generally circular base plate 30. The orbiting scroll 20 comprises a scroll wall 34 which extends perpendicularly to a generally circular base plate 36. The orbiting scroll wall 34 co-operates, or meshes, with the fixed scroll wall 28 during orbiting movement of the orbiting scroll. Relative orbital movement of the scrolls causes a volume of gas to be trapped between the scrolls and pumped from the inlet to the outlet.
In
In the single-start condition shown in
At least one single-start transfer flow path (shown by arrow 42) conveys fluid across the interruption 40 and the valve arrangement (described below) is operable to direct fluid along the or each transfer flow path in the single-start condition. The single-start transfer flow path 42 extends from three inlet ports 44 on one (upstream) side of the interruption 40 to an outlet port 46 on the other (downstream) side of the interruption. The benefit of providing a plurality of inlet ports 44 is to improve compression of the pumped fluid and its transfer across the radial wall to port 46. However, a single inlet port may be adopted as an alternative.
The single-start transfer flow path 42 may be formed by a duct extending between the inlet ports 44 and the outlet ports 46 at least partially through the scroll plate 30, 36 of the relevant scroll. In one arrangement, the duct is formed wholly within the scroll plate. In another arrangement, bores may be made through the scroll plate and pipe-work connected to the through-bores at the back of the scroll plate to form the duct.
Two further ports 48, 50 are shown in the fixed scroll plate in
In the multi-start condition shown in
The multi-start transfer flow paths 52, 54 are formed by ducts extending through one or both of the scroll plates and in this example, the ducts are formed in the fixed scroll plate. The duct of transfer flow path 52 extends from the inlet port 48 in scroll wrap I to the outlet port 46 in the successive scroll wrap II. The duct of transfer flow path 54 extends from the inlet ports 44 in scroll wrap II to the outlet port 50 in the successive scroll wrap III.
Comparing
Referring to
The valve member 58 is formed in this example by an elongate spool valve having three spools 60, 62, 64. The spool is fitted for longitudinal movement in a spool valve chamber 66. The spools are closely adjacent the spool valve chamber to reduce leakage. A controller 67 controls an actuator 69 for moving the valve back and forth in the chamber to slide the spools into different positions.
In the single-start condition shown in
Spool 60 is not required in this arrangement for directing fluid flow and is included to stabilize movement of the valve in the valve chamber. It can therefore be omitted. Other suitable valve arrangements will be apparent to those skilled in the art. For example a valve may be arranged to selectively block one of the two inlet channels in wraps I and II of a two-start pump. This embodiment could be achieved with a less complex valve, which would reduce the cost of implementation. Although this simplified approach would not deliver the superior ultimate pressure of a single start pump.
The single-start and two-start prior art pumps reduce pressure over an initial period to 100 mbar at a similar rate. However, the power consumed by the single-start pump is less than that of the two-start pump. Therefore, the hybrid pump adopts the single-start condition over this initial period for reduced power consumption. After the initial pressure decrease to 100 mbar, the two-start pump reduces pressure at a faster rate than the single-start arrangement. Therefore, the hybrid pump adopts the multi-start arrangement during evacuation of the chamber from about 100 mbar to about 0.01 mbar. It will be seen that the single-start pump can achieve a lower ultimate pressure of 0.005 mbar but with more power consumption than the two-start pump which achieves 0.01 mbar at ultimate with lower power consumption. Accordingly, below 0.01 mbar the hybrid pump can be arranged to adopt the single-start arrangement or the two-start arrangement, depending on the user's requirements, for example if the user requires a lower ultimate pressure or reduced power consumption.
The switching between single-start and multi-start condition may be performed manually by an operative who is monitoring the pump. Alternatively, one or more sensors may output one of pressure level, pressure gradient, power level, power gradient or any other suitable pump characteristic to the pump control for activating switching between conditions.
The above operation of the hybrid pump is only one of the ways in which the hybrid pump can be operated. For example, a pump operative may consider that conservation of power is most desirable. Alternatively, the operative may be more concerned with rate of pressure reduction that ultimate pressure. Accordingly, in its most general sense, the hybrid pump can be operated for controlling operation of the valve arrangement dependent on any one or more characteristics of the pump, including without limitation power, rate of pressure reduction and ultimate pressure. It would also be possible to provide pre-programmed operation modes to achieve, for example, fastest pump down, lowest power, best ultimate, longest tip seal life and other modes specified or programmed by the user.
The present embodiment is operative in a single-start condition or a multi-start condition. The term multi-start means two or more starts. Additionally, the pump can be configured to be operative in more than two conditions, for example, a single-start condition, a two-start condition and a three-start condition (or even more such conditions as required). If the pump were configured for a three-start condition, two single-start transfer flow paths would be required and three multi-start transfer flow paths would be required. These flow paths may be formed in one or both of the scroll plates. Further, in some applications, for example where ultimate pressure is not considered to be the most important characteristic, the pump may be configured without a single-start condition. In this regard, there may be a two-start condition and a three-start condition or any combination of multi-start conditions. In such a two-start/three-start arrangement, the single-start transfer flow path referenced 42 in the description of the earlier embodiment will not be required. The first two wraps in this arrangement will be similar to the prior art two-start arrangement shown in
Claims
1. A vacuum scroll pump comprising:
- a first scroll intermeshing with a second scroll and arranged so that, on relative orbital movement of the scrolls, fluid is pumped from an inlet of the scroll pump to an outlet of the scroll pump, wherein each of the first and second scrolls comprises a respective plurality of successive scroll wraps between the inlet and the outlet;
- a single-start condition in which fluid is pumped from the inlet to the outlet along a single flow path extending through each of the scroll wraps of the first scroll in succession;
- a multi-start condition in which fluid is pumped from the inlet along a plurality of flow paths which extend in parallel through radially adjacent scroll wraps of the first scroll and converge to a single flow path prior to the outlet; and
- a valve arrangement operable for switching the scroll pump between the single-start and the multi-start conditions.
2. The vacuum scroll pump of claim 1, wherein:
- the single flow path extending through each of the scroll wraps of the first scroll in succession includes at least one interruption for preventing fluid flow;
- the scroll pump further comprises at least one single-start transfer flow path for conveying fluid across the interruption; and
- the valve arrangement is operable to direct fluid along the at least one single-start transfer flow path in the single-start condition.
3. The vacuum scroll pump of claim 2, further comprising a plurality of multi-start transfer flow paths for conveying fluid across scroll walls between respective adjacent scroll wraps of the first scroll, the valve arrangement being operable to direct fluid along the plurality of multi-start transfer flow paths in the multi-start condition.
4. The vacuum scroll pump of claim 3, wherein each of the two intermeshing scrolls comprises a respective scroll plate, and wherein the single-start transfer flow path and the multi-start transfer flow paths are respectively formed by ducts extending through one or both of the respective scroll plates.
5. The vacuum scroll pump of claim 4, wherein the single-start transfer flow path extends from an inlet port on one side of the interruption to an outlet port on the other side of the interruption.
6. The vacuum scroll pump of claim 5, wherein each of the multi-start transfer flow paths extends from an inlet port in one of the respective plurality of successive scroll wraps of the first scroll to an outlet port in a successive wrap of the respective plurality of successive scroll wraps of the first scroll.
7. The vacuum scroll pump claim 6, wherein the inlet port of the single-start transfer flow path forms the inlet port of one of the multi-start transfer flow paths and the outlet port of the single-start transfer flow path forms the outlet port of another one of the multi-start transfer flow paths.
8. The vacuum scroll pump of claim 7, wherein the valve arrangement comprises a valve member fitted for movement between a first position that allows gas flow along the single-start transfer flow path and resists gas flow along the multi-start transfer flow paths in the single-start condition of the pump, and a second position that allows gas flow along the multi-start transfer flow paths and resists gas flow along the single-start transfer flow path in the multi-start condition of the pump.
9. The vacuum scroll pump of claim 8, wherein at least a portion of the single-start transfer flow path and at least a portion of at least one of the multi-start transfer flow paths are partially co-extensive and the valve member is fitted for movement in the portion of the flow paths which are co-extensive.
10. The vacuum scroll pump of claim 4, wherein each of the multi-start transfer flow paths extends from an inlet port in one of the respective plurality of successive scroll wraps of the first scroll to an outlet port in a successive wrap of the respective plurality of successive scroll wraps of the first scroll.
11. The vacuum scroll pump of claim 1, further comprising a plurality of multi-start transfer flow paths for conveying fluid across scroll walls between respective adjacent scroll wraps of the first scroll, the valve arrangement being operable to direct fluid along the plurality of multi-start transfer flow paths in the multi-start condition.
12. The vacuum scroll pump of claim 1, further comprising a controller configured to control operation of the valve arrangement dependent on one or more characteristics of the pump.
13. The vacuum scroll pump of claim 12, wherein the pump characteristics include one or more of power consumption, rate of power consumption change, pressure, or rate of pressure change.
14. The vacuum scroll pump of claim 13, wherein the controller is configured to select operation of the scroll pump in the single-start condition or the multi-start condition at any given pressure dependent on the rate of pressure reduction achieved in the single-start condition or the multi-start condition.
15. The vacuum scroll pump of claim 14, wherein the controller is configured to select operation of the scroll pump in the single-start condition or the multi-start condition at any given pressure dependent on the power consumed by the scroll pump at that pressure in the single-start condition or the multi-start condition.
16. The vacuum scroll pump of claim 13, wherein the controller is configured to select operation of the scroll pump in the single-start condition or the multi-start condition at any given pressure dependent on the power consumed by the scroll pump at that pressure in the single-start condition or the multi-start condition.
17. A vacuum scroll pump comprising:
- a first scroll intermeshing with a second scroll and arranged so that, on relative orbital movement of the scrolls, fluid is pumped from an inlet of the scroll pump to an outlet of the scroll pump, wherein each of the first and second scrolls comprises a respective plurality of successive scroll wraps of the first scroll between the inlet and the outlet;
- a first multi-start condition in which fluid is pumped from the inlet along a first plurality of flow paths which extend in parallel through radially adjacent scroll wraps of the first scroll and converge to a single flow path prior to the outlet;
- a second multi-start condition in which fluid is pumped from the inlet along a second plurality of flow paths which extend in parallel through radially adjacent scroll wraps of the first scroll and converge to a single flow path prior to the outlet, wherein the number of starts in the first multi-start condition is different from the number of starts in the second multi-start condition; and
- a valve arrangement operable for switching the scroll pump between the first and the second multi-start conditions.
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- International Search Report dated Jul. 29, 2013 in the counterpart PCT Application No. PCT/GB2013/051513, 3 pgs.
- Search Report under Section 17 mailed Nov. 6, 2012 in counterpart GB Application No. 1211997.0, 4 pgs.
- First Office Action and Translation thereof dated Jul. 31, 2015 in counterpart CN Application No. 201380035940.8, 14 pgs.
Type: Grant
Filed: Jun 10, 2013
Date of Patent: Mar 29, 2016
Patent Publication Number: 20150192125
Assignee: Edwards Limited (Crawley)
Inventors: Alan Ernest Kinnaird Holbrook (Pulborough), Miles Geoffery Hockliffe (Ringmer)
Primary Examiner: Theresa Trieu
Application Number: 14/411,556
International Classification: F01C 1/02 (20060101); F03C 2/00 (20060101); F03C 4/00 (20060101); F04C 2/00 (20060101); F04C 18/02 (20060101); F04C 28/06 (20060101); F04C 28/24 (20060101); F04C 23/00 (20060101);